1. Field of the Invention
This invention relates to marine cylinder oils containing overbased detergents for the lubrication between piston rings and cylinder walls in high output adverse environment engines, and to overbased calcium sulfonate detergents therefor.
2. Background and Discussion of Prior Art
Particularly high rates of wear occur in high output marine engines or oceangoing vessel diesel engines, and particularly when these adverse environment engines are operated on fuels containing significant amounts of sulfur and asphaltenes. The oils subject to these adverse cylinder and piston ring environments are known as marine cylinder oils or cylinder oils. It was therefore necessary for marine cylinder oils to meet diverse stringent requirements. Marine cylinder oils are, generally speaking, blends of a high viscosity base oil and a solvent neutral or paraffinic oil, with detergents such as an overbased calcium sulfonate and overbased calcium phenate.
Marine cylinder oils are consumed with each stroke at a typical rate of about 0.9 g/hphr (1.20 g/kwhr) while being subjected to a severe environment. The marine cylinder oils, unlike conventional lubricating oils, must perform extremely broad functions, including the ability to spread over the entire cylinder liner surface, the ability to resist the effects of temperature, pressure, oxygen, moisture, and combustion products, the ability to maintain an oil film between piston rings, piston and cylinder liners, and also the ability to prevent corrosive wear and resist oxidation under extreme conditions.
In addition to the foregoing stringent demands, the marine cylinder oil art greatly desired a low cost product particularly so because of the high level of consumption.
Reported test data suggests that cylinder liner wear and piston ring wear would decrease with increase in the marine cylinder oil viscosity. The art, was for the foregoing reasons, directed to additive packages for improving viscosity as well as other characteristics. Additives, however, are costly components.
Another prior art solution to achieve the requisite viscosity was to provide substantial amounts of a high viscosity lubricating base oil having a viscosity of at least about 430 to 850 mm2/s at 40xc2x0 C. (2000 to 4000 SUS at 100xc2x0 F.), in combination with the low cost, low viscosity, refined solvent neutral or paraffinic oil which has a viscosity of only about 117 mm2/s (500 SUS at 100xc2x0 F.). The high viscosity base oil, such as a bright stock oil, however, was more costly and less stable at high temperatures than the solvent neutral oil.
The art directed to lubricating oils required overbased detergents with improved filterability and reduced viscosity, and was therefore directed away from the use of high viscosity detergents. This prior art direction is discussed in U.S. Pat. No. 5,011,618, granted Apr. 30, 1991 to Papke et al and U.S. Pat. No. 4,387,033, granted Jun. 7, 1983 to Lenack et al.
The present invention provides improved marine cylinder oil viscosity with a reduction in the amount of the high viscosity base oil, thereby, achieving cost effectiveness.
The invention is, in one aspect, a novel overbased calcium sulfonate detergent which produces clear solutions in lubricating oil, has a TBN of at least about 400 (i.e. about 400 or more), and which has a viscosity of at least 180 mm2/s (180 cST) at 100xc2x0 C. Such calcium sulfonate detergents are particularly useful in marine cylinder oil compositions. The inventive detergents are especially useful in formulating marine cylinder oil compositions which comprise a blend of expensive high viscosity lubricating oil and lower cost low viscosity oil, where their high viscosity, when used alone or in combination with another high viscosity detergent such as an overbased calcium phenate, allows a commensurately proportional reduction of the high viscosity oil, relative to compositions prepared with prior art detergents, while maintaining a selected TBN and viscosity in finished oil composition.
Marine cylinder oil compositions formulated to specified viscosity and TBN specifications and employing a blend of two oils of substantially different viscosity constitute a further aspect of the invention. In such oils the weight percent of the higher viscosity oil in the blend is inversely commensurately proportional to the viscosity of the detergent. That is, for an amount of detergent calculated to provide a given TBN in the finished oil, the higher the detergent viscosity the lesser the amount of the higher viscosity oil is required to achieve a specified finished oil viscosity.
A method of preparing the high viscosity calcium sulfonate detergent of the invention constitutes a still further aspect of the invention.
The Marine Cylinder Oil
The term xe2x80x9csubstantially higherxe2x80x9d as used hereinbefore and hereinafter in the context of the difference between viscosities of two lubricating oils in a blend means that the viscosity of the higher viscosity oil is at least about 170 mm2/s at 40xc2x0 C. (800 SUS at 100xc2x0 F.) greater than the viscosity of the lower viscosity oil.
A cost effective way to achieve a desired finished marine cylinder oil viscosity is to blend relatively substantial amounts of an inexpensive low viscosity oil, suitably one having a viscosity of 195 mm2/s at 40xc2x0 C. (900 SUS at 100xc2x0 F.) or less, with an expensive high viscosity oil, such as a bright stock oil of about 430 mm2/s at 40xc2x0 C. (2000 SUS at 100xc2x0 F.) or more. The finished marine cylinder oils may contain a detergent component which is composed of up to 100% of the overbased calcium sulfonate of the invention. Optionally, the detergent component will contain a combination of a high viscosity overbased calcium sulfonate of the invention and a high viscosity overbased calcium phenate. Insofar as the high viscosity overbased phenate is generally more costly than the high viscosity overbased sulfonate, a blend of the phenate and sulfonate provides optimization of both viscosity and economy.
The marine cylinder oil of the present invention, in an exemplary embodiment, comprises a blend of a solvent neutral paraffinic or like oil having a relatively low viscosity of no more than about 117 mm2/s at 40xc2x0 C. (500 SUS at 100xc2x0 F.), a bright stock or like oil having a relatively high viscosity of at least about 430 mm2/s at 40xc2x0 C. (2000 SUS at 100xc2x0 F.), and a detergent component comprising a high viscosity overbased calcium sulfonate detergent of the invention, optionally in combination with a calcium phenate detergent.
The marine cylinder oil compositions suitably comprises no more than about 35% by weight, and preferably no more than about 30% by weight, of the high viscosity oil, and yet achieves a desired marine cylinder oil blend viscosity of at least about 15 to 25 mm2/s or more at 100xc2x0 C. at a specified TBN of at least about 10 and preferably at least about 50 to 90 or more. The oil composition TBN is determined by the amount of the overbased calcium sulfonate and, if used, the overbased calcium phenate used in the composition.
The overbased detergent is present in the marine cylinder oil in amounts of about 2 to 25% by weight and preferably about 10 to 20% by weight. Where a combination of detergents is used, the total detergent present in the marine cylinder oil is preferably in an amount of about 10 to 25% by weight.
The low viscosity solvent neutral oil preferably has a viscosity of no more than about 195 mm2/s at 40xc2x0 C. (900 SUS at 100xc2x0 F.), and especially suitably has a viscosity of 500 SUS at 100xc2x0 F. (117 mm2/s at 40xc2x0 C.) or less. The relatively low cost, low viscosity solvent neutral oil may be present in the marine cylinder oil in amounts greater than about 40% by weight, and preferably 80% by weight or more, where the high viscosity overbased detergent is present.
It has-been found that the marine cylinder oil of the present invention achieves a comparable viscosity to that of prior art blends but can reduce the high viscosity lubricating oil (e.g. bright stock oil) component- requirement by at least 10% by weight, and generally from 12 to 16% by weight or more. This reduction can substantially lower the cost of the finished marine cylinder oil.
In the finished marine cylinder oil, other additives may be included such as dispersants, pour depressors, antioxidants, oleaginous agents, antifoamants and mixtures thereof. A preferred dispersant is an alkyl succinimide, which is added in amounts of from about 1 to 2%. A still further specific additive which may be included is a polymeric dimethyl silicone antifoamant. The silicone polymer antifoamant is desirably employed in amounts of about 100 to 1000 ppm.
The marine cylinder oil of the present invention may preferably be substantially free of costly viscosity index improvers.
The High Viscosity Overbased Calcium Sulfonate
The high viscosity overbased calcium sulfonate detergents of the invention have a viscosity of about 180 mm2/s or higher, suitably up to 800 mm2/s at 100xc2x0 C., and preferably from 180 to 500 mm2/s at 100xc2x0 C.
The inventive overbased calcium sulfonate is suitably formed from a mixture of a sulfonic acid, a hydrocarbon solvent, an alcohol, water and adding a stoichiometric excess of a calcium hydroxide above that required to react with the sulfonic acid, and carbonating the mixture with a carbon dioxide source at a specific temperature range of 27 to 57xc2x0 C. (80xc2x0 to 135xc2x0 F.), which after filtration and stripping produces a 400 TBN calcium sulfonate having an high viscosity of from about 180 to 500 mm2/s or higher at 100xc2x0 C.
The process for preparing the high viscosity overbased calcium sulfonate includes the steps of: providing a sulfonic acid to a reactor, adding a lime reactant (i.e. calcium hydroxide or calcium oxide) to the reactor for neutralization and overbasing, adding a lower aliphatic C1 to C4 alcohol and a hydrocarbon solvent, to form a process mixture in a reactor which is suitably at a temperature of up to about 27xc2x0 C. (80xc2x0 F.), injecting carbon dioxide into the reactor at an initial temperature of 43-54xc2x0 C. (110-130xc2x0 F.) until substantially all of the lime has been carbonated while maintaining the exotherm of the reaction to between 27xc2x0 and 57xc2x0 C. (80xc2x0 and 135xc2x0 F.), and preferably 43xc2x0 to 52xc2x0 C. (110xc2x0 to 125xc2x0 F.), adding a quantity of oil to the reacted mixture to form a product mixture, clarifying the product mixture by filtering solids and distilling off the volatile hydrocarbon solvents and water, so that a bright, clear, highly overbased, high viscosity calcium sulfonate is formed.
The sulfonic acid may be a natural or synthetic sulfonic acid and may include a calcium salt of the sulfonic acid. In one important aspect, the present invention provides that at least 50%, and preferably 80% or more by weight of the sulfonic acid, be a natural sulfonic acid. The sulfonic acids are prepared by treating petroleum products with sulfuric acid or SO3. The compounds in the petroleum product which become sulfonated contain an oil solubilizing group. The acids thus obtained are known as petroleum sulfonates. Included within the meaning of sulfonates are the salts of sulfonic acids such as those of alkylaryl compounds. These acids are prepared by treating an alkylaryl compound with sulfuric acid or SO3. At least one alkyl substituent of the aryl compound is an oil solubilizing group as discussed above. The acids thus obtained are known as alkylaryl sulfonic acids and the salts as alkylaryl sulfonates. The sulfonates wherein the alkyl is a straight-chain alkyl are the well known linear alkyl sulfonates (LAS). The acids are then converted to the metal salts thereof by neutralization with a calcium compound, particularly including calcium hydroxide.
The sulfonates in addition to having a high viscosity are highly overbased. Overbased materials are characterized by a metal content in excess of that which would be present according to the stoichiometry of the calcium and the particular organic compound said to be overbased. Thus, an oil soluble monosulfonic acid, when neutralized with a calcium compound, will produce a normal sulfonate containing one equivalent of calcium for each equivalent acid. In other words, the normal sulfonate will contain one mole of calcium for each two moles of the monosulfonic acid.
By modifying well-known carbonation procedures, the novel high viscosity overbased sulfonate detergents of the invention can be obtained. These overbased materials can contain amounts of metal many times in excess of that required to neutralize the acid. The highly overbased calcium sulfonates have TBN (ASTM D 2896) values of about 400 or more, suitably up to about 500.
The lime reactant may encompass hydrated lime in the form of calcium hydroxide. Typically, the lower aliphatic alcohol reactant may be an alcohol selected from the group consisting of alkanol of from 1 to 4 carbons, and in a preferred embodiment the lower aliphatic alcohol is methanol. The quantity of C1 to C4 alkanol or lower aliphatic alcohol added to the reaction mixture is in amounts such that the amount of the total promoter is less than about 15% by weight of the yield of finished product formed in the last step of the process. The C1 to C4 alkanol is present in the range of about 8% to 10%, and usually about less than 12%, of the finished product.
The petroleum hydrocarbon solvent particularly includes a paraffinic solvent having a boiling amount range of 70xc2x0 to 166xc2x0 C. (160xc2x0 to 330xc2x0 F.).
High Viscosity Overbased Calcium Phenate
In addition to the high viscosity overbased calcium sulfonate of the invention, a high viscosity overbased calcium phenate may also be present, in combination with the sulfonate, in the marine cylinder oil. The overbased calcium phenate has a viscosity of at least about 180 mm2/s at 100xc2x0 C., preferably 200 to 800 mm2/s at 100xc2x0 C. more preferably 250 to 600 mm2/s at 100xc2x0 C. and most preferably 250 to 400 mm2/s at 100xc2x0 C.
Methods for producing useful overbased calcium phenates are disclosed in U.S, Pat. No. 5,281,345, granted January 25, 1994, to Crawford ct al., EPO 0 354 647, published Feb. 14, 1990, and U.S. Pat. No. 4,104,180, granted August 1, 1978 to Bumop (xe2x80x9cBurnopxe2x80x9d). While high viscosity overbased detergents are known in the art, they are often avoided. Bumop, by way of example, includes a discussion directed to avoiding the production of such high viscosity phenates.
While the invention is principally described for high viscosity sulfonates and phenates, high viscosity carboxylates are also within the contemplation of the invention. The sulfonates, phenates and carboxylates are present in the marine oil in the form of their Group I and Group II metal salts. Group I metals useful in forming the detergent include lithium, sodium and potassium. Group II metals useful in forming the detergent agent include magnesium, calcium and barium, of which calcium is most preferred.
The present invention is further illustrated by the following examples, which are not, however, to be construed as limitations. All references to xe2x80x9cpartsxe2x80x9d or xe2x80x9cpercentagesxe2x80x9d are references to parts or percentages by weight unless otherwise expressly indicated.